1. Field of the Invention
This invention relates to an absorptive article comprising a combined non-woven fabric which is bulky, and has a good hand feeling and touch, and is used as a surface material. More particularly, the present invention relates to an absorptive article which is superior in the permeation-absorption and spot-absorption of a body fluid and in dryish feeling, and in the property of small back flow of the permeated body fluid all of which are required of absorptive articles such as disposable diapers and sanitary napkins.
2. Description of the Related Art
Various embodiments of absorptive articles formed so as to absorb body fluids such as urine, sweat, and blood nave been well known. In general, absorptive articles are composed of a liquid permeable (pervious) top sheet, a liquid impermeable back sheet and an absorptive body arranged between the top sheet and the back sheet. A single or a plural number of additional layers are sometimes additionally interposed between the above layers. Such additional layers may rapidly transport the body fluid. As the surface materials for the top sheet or back sheet, knit or woven fabrics, non-woven fabrics, films or composite materials thereof are used, and the required performances are varied. Since the surface materials touch human skins, bulkiness, excellent hand feeling, and good touch have been required. Further, for the top sheet, a high permeation-absorption and spot-absorption of a body fluid, a dryish feeling, and the property of a small back flow of the permeated body fluid have been required.
Since long fiber non-woven fabrics obtained according to a technique represented by a spun bonding process have a higher tenacity and are relatively cheap as compared with short fiber non-woven fabrics, the former have been used for various applications. However, the long fiber non-woven fabrics are inferior in the hand feeling as compared with short fiber non-woven fabrics, and in particular, when the former are used for the surface material of absorptive articles, it shows a drawback that they are inferior in the feeling such as the feeling when touched to skin. The reason that the feeling of the long fiber non-woven fabrics is inferior lies in that no crimp is developed in the long fibers from which the fabrics are formed, the apparent density is high, and thus the air content in the fabric is low. Accordingly, it can be considered that if crimps are developed in the long fibers, a long fiber non-woven fabric having a superior feeling can be obtained. However, it has been found that long fibers having crimps are difficult to effect uniform spreading, and in the case of long fibers having latent crimps, shrinkage occurs in the lengthwise direction of the long fibers when crimps are developed, whereby homogeneous long fiber non-woven fabrics can sometimes not be obtained.
On the other hand, short fiber non-woven fabrics obtained according to technique represented by a carding process are excellent in homogeneity and composed of crimped short fibers. Accordingly, they are bulky and have a good feeling such as to touch. However, since the short fiber non-woven fabrics are composed of an assembly of short fibers, they have a low strength as compared with long fiber non-woven fabrics, and have a drawback of readily being broken when they are used as a surface material of absorptive articles.
As described above, both long fiber non-woven fabrics and short fiber non-woven fabrics have merits and demerits. Thus, it has been difficult to make the merits coexistent in a single fiber layer. As the technique for making the merits of long fiber non-woven fabrics and short fiber non-woven fabrics coexistent, lamination of a long fiber non-woven fabric and a short fiber non-woven fabric is generally performed. Such a technique, for example, Laid-open Japanese Patent Publication No. Hei 6-136654 discloses a laminated or combined non-woven fabric obtained by laminating a long fiber non-woven fabric and a short fiber non-woven fabric, followed by subjecting the resulting laminate to a high pressure water steam treatment. However, since not only the short fiber non-woven fabric disclosed in the above technique, but also most of short fiber non-woven fabrics are obtained according to a carding process, short fibers which form the non-woven fabric are arranged in the lengthwise direction, i.e. mechanical direction of the non-woven fabric, whereby they are very anisotropic and inferior in the isotropy. Accordingly, when such non-woven fabrics are used as a surface material of absorptive articles, a capillary-like function is exercised in the short fiber non-woven fabrics and the laminated non-woven fabrics in the mechanical direction of the non-woven fabrics, and thus the body fluid is easily spread in the arranged direction of fibers at the time of absorption of the body fluid. Accordingly, the non-woven fabrics have drawbacks that they are not only inferior in the permeation-absorption, but also they easily retain the fluid. Even when they are subjected to a high pressure water stream treatment, the arrangement of the short fibers, after all, depend on the processing process of fibers into a non-woven fabric, i.e. a carding process. Thus, the short fiber non-woven fabrics and their laminated non-woven fabrics are as yet liable to retain the fluid, and the permeation-absorption and the spot-absorption of the body fluids is poor. Further, since the laminated non-woven fabric according to this technique has been subjected to a high-pressure water stream treatment, it has a high apparent density and is liable to cause the back-flow. Accordingly, when such a laminated non-woven fabric is used as a surface material of absorptive articles such as disposable diapers, sanitary napkins, particularly as top sheets, good permeation-absorption and spot-absorption of body fluid such as urine, sweat, and blood, dryish feeling and a small back flow of permeated body fluid which are inherently required of absorptive articles is unsatisfactory.